This invention relates to a fuel injection controller for an internal combustion engine which controls the amount of fuel which is injected into an engine based on the air pressure within the intake pipe of the engine. More particularly, it relates to a fuel injection controller which employs an inexpensive, low-resolution A/D converter.
A conventional fuel injection controller for an internal combustion engine has an air pressure sensor which senses the air pressure within the intake pipe of the engine and generates a corresponding analog output signal. This output signal is converted into a digital pressure signal by an A/D converter, and based on the value of the digital pressure signal and other parameters, a control unit controls the operation of fuel injectors so as to obtain a suitable air/fuel ratio.
During idling of a typical engine, the pressure in the air intake pipe is around 250 mm Hg. In order to detect the air pressure with a resolution of 1% or less, the resolution of the A/D converter must be at most 2.5 mm Hg/bit. If the full-scale reading of the A/D converter is to be 950 mm Hg, the A/D converter must generate an output having at least 9 bits. However, 9-bit A/D converters are not generally available on the market, so instead, a conventional fuel injection controller employs a 10-bit A/D converter, which is easily obtainable.
However, a 10-bit A/D converter is expensive, and therefore a conventional fuel injection controller is also expensive.